CCP High Frequency Coupler Kit GRAS 43BA-2 1/4”

Introduction

• The GRAS 43BA-2 is a high frequency 1/4″ 0.4cc coupler kit for test of hearing aids at frequencies up to 16 kHz. It is a complete kit with a 1/4″ Pressure Microphone and a 1/4″ Preamplifier with BNC connection and the same adapters known from the reference 2cc coupler. It is easy and safe to handle and calibrate because the microphone grid does not have to be removed for mounting or calibration.

Typical applications and use

• It is designed in accordance with the Technical Specification “IEC TS 62886:2016 Electroacoustics – Hearing aids – Method for measuring electroacoustic performance up to 16 kHz”. It meets the need for an accurate and repeatable measurement method that can be used by designers of hearing aids and hearing aids receivers, and by fitters of hearing aids. IEC TS 62886 can be bought from the IEC webstore, https://webstore.iec.ch/publication/25718.
• The small volume in combination with the 1/4″ microphone results in a wide frequency range that makes it useful for high-frequency diagnostics. The extended frequency range also ensures that it is a future proof choice for high-frequency testing of wide-band hearing aids.
• Its 0.4cc volume is a well defined cylinder where the diaphragm of the microphone is flush with the bottom of the cylinder. The cylinder is machined to within ±2% of the nominal 0.4cc volume. The exact volume for each individual coupler is stated in the accompanying calibration chart. The performance of the 0.4cc coupler can therefore be accurately simulated, and it can easily be a part of a complete simulation model.
• The 43BA is designed for repetitive use and is equally suited for research, quality assurance and production test applications.

Design

• The 43BA is developed with and for the hearing aids industry. Through our close collaboration with global leaders within the industry, we found an increasing need for test of modern hearing aids at high frequencies. In accordance with the intentions of the previously mentioned IEC Technical Specification GRAS has designed a coupler kit capable of delivering differentiated and reproducible data up to 16 kHz.  
• Because of the small volume, the measured sound level from the 0.4cc coupler is 13.5 dB higher than with a 2cc coupler. This increase in level improves the signal-to-noise ratio compared to what is normally achievable with the 1/4″ microphone used.
• Another benefit of the small volume and the 1/4″ microphone is the fact that the resonance frequency at 30 kHz is so high that it does not interfere with measurements in the audible frequency range. Therefore it can be used for measurements up to 16 kHz, one octave higher than achievable with the standardized 2cc coupler.
• The 43BA-2 is designed to perform optimally with the GRAS 40BD Prepolarized Pressure Microphone, which is ideally suited for for sound measurements at high levels and high frequencies. It has a wide dynamic range for measuring sound pressure levels up to 168 dB. The preamplifier is the  GRAS 26CS CCP Standard Preamplifier, Very Short. The 26CS is a small robust unit short enough for use in confined spaces like anechoic test chambers. It has a very low inherent-noise level, a wide dynamic range and a frequency response from below 2 Hz to above 200 kHz.
• The microphone set is locked and kept firmly in position by a very precise locking mechanism, that automatically centers and  locks the microphone at the same time, eliminating the risk of measurement errors caused by incorrect positioning of the microphone. An O-ring ensures a tight sealing of the microphone. The microphone set can easily be removed for sensitivity calibration – without tools. There is never any need for removing the protective grid, neither for use, calibration or other handling of the microphone.

Compatibility

• The GRAS 43BA-2 requires a power module or measurement  instrumentation input that that can provide a constant current of app. 4 mA. The microphone set requires a Microdot-BNC cable that is part of the delivery. Various extension cables are available. The 0.4cc coupler housing fits all GRAS 1/2″ 2cc standard ear mould and tube adapters.
• System verification
• For daily verification and check of your measurement setup we therefore recommend using a sound source like the GRAS 42AB Sound Calibrator. For proper sensitivity calibration we recommend using a reference sound source like the GRAS 42AP Intelligent Pistonphone.